Classy Nemesis

How to Overfix Your Commodore 64 Keyboard (and Other Problems)

Jonathan Prusik — Thu, 22 Jan 2026 10:58:00 -0500

I pulled my secondary (now only) Commodore 64 out of storage last week and found that some of the keys didn't work. So naturally, I started throwing spaghetti at the wall, trying everything suggested from the search results of "commodore 64 keyboard doesn't work":

reflow the wires on the keyboard PCB interface
clean all the keypad interfaces on the PCB
re-tension the keyboard key springs
"sand" down the keypad conductive rubber
paint graphite powder onto the keys conductive rubber

Note, to get to the keyboard PCB, you have to desolder the capslock switch (the pins connect on the backside of the board), so (before I got smart) I was desoldering and resoldering the switch after each of those "fixes", thinking "surely this time, I've solved it".

After putting it all together and taking it apart more times than I'd like to admit, I got (the aforementioned) smart and started debugging:

I tested continuity from the keyboard pads on the PCB to the cable interfaces (all good!)
I tested the resistance of the rubber pads (all good!)
I tested continuity of the cable itself (all good!)

That left the motherboard PCB as the only culprit, but that didn't make sense because none of the search results I had looked at said anything about the mobo.... OH NO! Do I have a bad chip somewhere???

Before I panicked, I made some notes; only some keys failed, and I already knew continuity from the keyboard through the cable was good. I looked up the keyboard matrix for the C64 keyboard:

Ah, so these keys share a particular madness. Namely, they belong to a shared pin. After tracing the cable back I tested the specific cable again, moving it around while doing so, in case it had a weird crimp or something. My multimeter gave it continuity beeps the whole time, so now I was able to rule out the entire top "chonk" (the technical term, I'm sure) of the C64, which left me... back at the motherboard. I was now quite annoyed because I was not eager at all to remove the motherboard and test components.

Before resigning myself to this endeavor however, I decided to first test continuity from the header pins on the motherboard (where the keyboard cables connect) to various points on the board. Aaaaand, since I had already identified the problematic pin, I could start there. I picked a nearby via and touched the pin, and it wobbled. After a few more pokes and a few more wibbly-wobbles (also a technical term), the issue was clear; the header pin had come loose (cold-solder joint?) and was freely sliding in the post hole. A quick clean and re-solder with fresh material, and the wibbly-wobbles were gone. Unsurprisingly, this immediately resolved all issues and the keyboard was restored to full functionality.

It is here at the end of this tale where one might examine, with humbled reflection, the virtues of methodology vs blindly applying a hefty smattering of unvetted advices across the canvas of your problems. One might even develop some narrative tissue around a more profound societal observation, perhaps concerned with the modern baggages of humanity's unyielding addiction to its entirely manufactured concept of "progress", even at the cost of its own soul.

But I won't do that, because less than a week later, I was addressing a new issue with the same directionless, expectant lack of approach. Clearly, knowing the lesson isn't the same as internalizing it.

References (and other helpful links):

(Video) Commodore C64 keyboard - how to repair hard to press keys

(Video) C64 Keyboard restoration. Revive key response

Case Studies in Retro Computer Repair (#4): Diagnosing and Fixing a Commodore 64 with Keys that Don’t Work and no Sound

The Commodore-64 Keyboard

Repairing the GB Smart 32M; So Bad it Goes Past Good and Back to Bad Again

Jonathan Prusik — Tue, 14 Mar 2023 10:58:00 -0400

In the past few years, I've really enjoyed developing my electronics repair hobby. What started as simple clean up here and there has escalated to board repair, component replacement, and improvised upgrades. I even acquired a hot air rework station, which has been fantastic for some very specific tricky situations (usually with surface mounted components / diodes). In the past I'd sometimes find myself stymied by obstacles and unsure of how to go about debugging an issue or repairing damages. But, the Internet has a kind side, and the communities of like-minded tinkerers and repair-ists are generous with sharing knowledge (I'm a big fan of ThePostApocalypticInventor, OddTinkering, Tronicsfix, and in particular, StezStix, who has a cheeky humility that is terribly endearing).

That said, I haven't bothered to write about most of my repairs because they've been either basic and uninteresting, or otherwise well-documented on the world wide intertubes.

GB Smart 32M

As best as I can determine, the GB Smart 32M is a budget-minded, barebones Gameboy flashcart mass-produced in China. It seems to be best known as the common bootleg distribution of the excellent homebrew program LSDJ. And, as this article linked by the LSDJ website points out, "...these cartridges are usually very low quality".

This $5 thrift store purchase did not disappoint in that regard as, while it functioned appropriately upon powering on, even a casual glance at the cart revealed significant corrosion materials on the pin interface that would not only inevitably fail in the near future, but which would also be an unwelcome contact with any console. With no screws visible, I initially tried to pry open the cart, assuming it utilized internal plastic clips often used in form-minded devices. When that did not work, I explored the "Warranty Seal" on the back; with the critical screw revealed, my journey finally began.

I'm sure the RMA process for this is rock-solid.

The Problem

Once the board had been removed, I gave it a quick rinse with 99% isopropyl alcohol and stuck it under the digital video microscope I have on hand. It became clear very quickly that either the cart had experienced extensive liquid exposure or the materials used in the PCB were breaking down. Aided by the microscopic view and a small pick, I probed and removed corroded materials from the board (it turned out nearly every pin interface pad was lined with corrosion). Exploring the board further, I discovered many of the traces had lost their masking and on the back of the board, one trace and via in particular had nearly completely corroded away (though miraculously still had continuity). Further examination revealed many places on the PCB where the factory masking was delaminating from the copper beneath. It was pervasive enough that I began to suspect a defect in the materials rather than water damage.

The Solution

I began work on the board by lightly scraping off the loose masking. Much of it came off all too readily with a wipe of isopropyl-soaked cloth, but using my pick, slight pressure would peel away the remaining problematic areas, where the properly adhered sections remained:

The delaminated masking has a slight discoloration (this is probably the worst case of this that I've encountered thus far).

For the heavily corroded trace, I applied some flux and re-soldered the connection to prevent further corrosion (and retested continuity). If the trace had lost continuity entirely (or if it does in the future), I probably would have bridged the circuit with a small length of wire or copper tape.

With everything wiped down and cleaned up, I used a small paintbrush to apply a fresh coat of "Mechanic" brand solder masking on the newly exposed copper and left it under a UV light for a couple minutes to cure.

Before masking (front)	After masking (front)
Note the exposed traces at the bottom corners and right and left of the board.

Before masking (back)	After masking (back)
On this side, we again have exposure on the left and right of the board. The corroded trace is soldered to the right of the screw mount hole.	Re-masking the exposed copper helps prevent future corrosion.

The results are a bit underwhelming, but I'm now more willing to insert this ~~sketchy bootleg~~ confidence-diminishing cartridge into my game systems without worry that I'll end up with corrosive materials transmitted to the console pins.

While this whole endeavor could be viewed (rightfully so) as a warning as to the poor quality and longevity of these cheap bootleg carts, it's still worth noting that I've also seen the issues documented here (albeit to a lesser degree) in official cartridges I've picked up over the years. That said, oftentimes a cart that has trouble booting only needs a little attention to the board before it's back up and running perfectly.

Repairing the Cybiko, a Future Device for 90s Teens

Jonathan Prusik — Sun, 12 Mar 2023 14:07:00 -0400

ProTip! The model used for the replacement part described in this project can be found on my Printables account:

Cybiko battery compartment cover

One thing I've grown to appreciate about older electronics is how generally repairable they are. Where an increasing number of modern devices are designed to be disposed of when even a single otherwise replaceable component fails (to see how far this has gone, check out the battery replacement guides out there for each successive generation of iPod). But even beyond the luxurious and forgiving space of 70s and 80s PCBs, a little research, skill, and a willingness to experiment can often yield satisfying results.

Enter a recent visit of mine to a local thrift store, and an inevitable $5 dollar purchase:

Wrapped in all the attitude of late 90s translucent neon plastic, I found this curious artifact mislaid in a bin of calculators. I had almost dismissed it as another inconsequential electronic pocket PDA (as were the fashion in the 90s), until I noticed the label on the back with the big bold (ALL-CAPS) letters: "FREE GAMES", followed by a web address.

This is of course, for me, a clarion call I may not ignore.

Some Background

The Cybiko is an somewhat obscure handheld device targeted toward teens that was released near the start of the fresh new millennium (the year 2000, for the temporal passengers out there). The base features are unremarkable; standard calculator and address book PDA fare. But in nearly all other ways, the Cybiko was ahead of it's time. Where it's popular contemporaries (think Nintendo GBA and Bandai WonderSwan) were nowhere near ready for the digital revolution of communication and commerce the Internet had begun to deliver, the Cybiko came equipped with wireless P2P (and group) messaging and data transfer. It also provided online games and updates to download to your device; a novelty (particularly for game systems) at the time that would eventually become standard. Curiously, while it seems to be remembered by many, I wasn't able to find much information about it beyond the regurgitation of the same high-level information found on Wikipedia (excepting one decent video). XKCD has us covered though, of course.

The Problem

After I understood what this thing was, I was sufficiently motivated to get it running. First up, the common dread problem of older electronics; the batteries:

The Cybiko has these "GP7M Size F6" rechargeable batteries, which are a bit flat and rectangular, but fortunately somewhat standard / still available. The batteries were intended to be left in the device for charging, so I'm appreciative that the door to the battery compartment is easily accessible without disassembly. That's where the good times end however, because the battery terminals in the rear enclosure have two prongs that, when the system is assembled, press against two pads on the board mounted to the front enclosure. This is apparently a common point of disaster with the Cybiko since, when the (possibly dodgy) batteries inevitably failed, the subsequent leakage would follow the terminal prongs and damage the board. In some cases, the damage was extensive enough to reach nearby chips and render the unit irreparable.

My unit had indeed suffered this fate, but after some careful cleaning with white vinegar (to neutralize the alkaline battery "acid") followed by 99% isopropyl alcohol to clean the remaining residue, I was able to verify functional continuity with my multimeter and some temporarily soldered wires from the board pads to the battery terminals. Normally, this is where I'd order new batteries, but I had a problem: I did not have a charger with the correct barrel size, much less proper power delivery (never mind that I'd ultimately be inviting the same battery failure scenario in the future). Since I had already decided I was not going to sink any more money into this project (a trap I've fallen into many times when making repairs), I decided some unconventional solution-ing was in order.

The Solution

Rechargeable battery tech has come a long way, but for my part, I'm rarely pleased to see some non-standard battery format inside an aging device. I've begun to favor devices with AA/AAA compatibility for their historical ubiquitousness without sacrificing recharge-ability (for me, the convenience of not having to pop out depleted batteries and pop in charged ones is rarely worth the tradeoff in device longevity). The biggest offender of this (in my opinion) is the Sony PSP, which not only had it's own (required) logic board, but a "spicy pillow" failure rate you could almost set a clock to (a problem which continues to plague after-market solutions to this day).

It is because of this and a suggestion by a Cybiko enthusiast blog post that I began to test powering the device with AAA batteries. After some soldering and fresh rechargeables, I hit the power switch:

The screen blinked on and suddenly, I was in business! Unfortunately, wires and batteries hanging all about was not conducive to regular play, so I began to ponder how I might attach this external battery compartment to the Cybiko so that it would be out of the way while serving it's purpose.

As I've previously mentioned, my dilemma with 3D printing is that it has quickly become my de facto tool for problem solving. This case was no different, and after some quick modeling and a few iterations, I had a new battery door for the Cybiko that allowed me to mount the new battery compartment.

At this point I was pleased; there was basic usability (lack of elegance notwithstanding) at no extra cost and my modifications were all easily and non-destructively reversible if I ever desired to return the unit to it's original state.

I began to play some of the included games, but then noticed the Cybiko was not emitting any sound. After checking the system settings, I concluded that the speaker had failed. It might have happened when I originally opened the unit, but re-soldering the contacts yielded no success. Stymied, I stepped away for a few days while I worked on other things. I was working on a GBA SP repair when I realized the speaker (on my nonfunctional donor SP) was about the right size to replace the Cybiko's original one. A quick solder and voila; the Cybiko began to sing again!

The Future, Here

Unfortunately, the Cybiko employs a proprietary data port and the cables for the port are rare, expensive, and apparently somewhat fragile. This means that I probably won't be loading any of those "FREE GAMES" preserved from the original Cybiko website any time soon. However, there is a solution to this from Kevin Norman, who worked out how to create a homebrew serial interface. This wasn't something I was feeling motivated to undertake at this point, but I'll throw up an update here if I do.